1. Field of the Invention
The present invention relates to a development device used in an image forming apparatus such as an electrophotographic copying machine or a printer. Particularly, the invention relates to improvements of a development device which includes a development unit that makes an electrostatic latent image on an image bearing member visible and a toner supply unit which can supply at least toner to this development unit, and a process cartridge and an image forming apparatus using this development device.
2. Background Art
Conventionally, for example, an electrophotographic image forming apparatus usually adopts a type in which an electrostatic latent image formed on an image bearing member such as a photoconductor drum is toner-developed (made visible) by a development device, and this toner image is transferred onto a transfer medium such as paper or an intermediate transfer member by a transfer device, while residual toner on the image bearing member is picked up by a cleaning device.
As the development device, as shown in FIGS. 18 and 19, a development device 500 has been already provided, which includes a development unit 510 in which developer composed of toner and carrier is housed and used for development, and additionally includes, in order to prolong lift of this development unit 510, a developer supply unit 520 which supplies the developer for the consumed amount of the developer used in the development unit 510 (refer to JP-A-2001-305861, JP-A-10-239970 and JP-A-11-44997).
In a development device shown in JP-A-2001-305861, of the conventional development devices of this type, the development unit 510, as shown in FIG. 18, includes a development housing 511 opposed to an image bearing member 501 such as a photoconductor drum, a developer housing room 512 in which developer G composed of toner and carrier is housed is provided in this development housing 511, a development roll 513 is arranged at the portion faced to an opening of this development housing 511, and further agitation-transportation augers 514 and 515 by which the developer G is agitated and transported are provided in the developer housing room 512.
On the other hand, the developer supply unit 520 includes a supply container 521 in which developer composed of toner and carrier is housed, communicates this supply container 521 with the development housing 511 through a communication duct 522, and can supply the developer in the supply container 521 by dropping by gravity to the upside of the developer G housed in the developer housing room 512.
In FIG. 18, the developer supply unit 520 includes a pick-up container 530 by which the developer G that has deteriorated in the developer housing room 512 can be picked up, and communicates this pick-up container 530 with the developer housing 511 through a communication duct 531.
In developing devices shown in JP-A-10-239970 and JP-A-11-44997, a developing unit 510 is nearly similar to that described in JP-A-2001-305861. However, a developer supply unit 520, as shown in FIG. 19A, includes a supply housing 541 that uses a part of a development housing 511 of the development unit 510 as a partition wall 550, includes in this supply housing 541 a developer supply room 542 in which supply developer is housed, includes an agitator 543 for agitation and transportation in this developer supply room 542, and further includes a developer supply mechanism and a developer pick-up mechanism on the developer unit 510 side of this developer supply room 542.
Here, in the developer supply mechanism, as shown in FIGS. 19A and 19B, a developer supply path 545 is provided by a path partition wall 544, a supply auger 546 is provided in this developer supply path 545, and a supply port 547 is formed in the partition wall 550. This supply port 547, in order to supply the developer smoothly without receiving pressure of the developer G from the developer housing room 512 side, is provided in the higher position than an axial center of an agitation-transportation auger 515, and preferably in the higher position than the surface position of the developer at the portion where the agitation-transportation auger 515 is provided.
On the other hand, in the developer pick-up mechanism, as shown in FIG. 19C, a developer pick-up path 555 is provided by a path partition wall 554, a pick-up auger 556 is provided in this developer pick-up path 555, and a pick-up port 557 is formed in the partition wall 550. This supply port 557, in order to increase the developer pick-up power from the developer housing room 512, is provided in the lower position than the axial center of the agitation-transportation auger 515.
However, any developing devices (including the developer supply unit) in JP-A-2001-305861, JP-A-10-239970 and JP-A-11-44997 adopt a system in which the supply developer is supplied onto the developer housed in the developer housing room of the development unit.
At this time, since the supply developer has a high concentration, and a filling rate of toner is higher than that of carrier, specific gravity of the supply developer is usually smaller than that of the developer in the developer housing room. Under such the state, when the supply developer is supplied onto the developer in the developer housing room, the supply developer enters a state in which it floats on the existing developer. Even in case that the developer is agitated and transported by the agitation-transportation augers 514 and 515, such a technical problem exists that the supply developer is not mixed sufficiently with the existing developer, or it takes time till the supply developer is mixed.
Regarding this technical problem, particularly, in case that the supply developer is only toner, bad agitation and mixing of the supply developer is easy to appear remarkably, because difference in specific gravity between the supply developer (toner) and the existing developer (toner and carrier) becomes large.
As a measure of this technical problem, a technology has been already proposed (refer to, for example, JP-A-10-142916). In this technology, in a type including a development unit and a developer supply unit (toner supply unit), a sub-room is provided adjacently to a developer housing room of the development unit, an agitation-transportation auger is provided in this sub-room, toner supplied from a toner supply port of the toner supply unit is caused to fall in the sub-room to be previously agitated and mixed by the agitation-transportation auger, and thereafter the toner is supplied to the developer housing room.
However, in this type development device, since the previously mixing mechanism (sub-room+agitation-transportation auger) is added to the development unit side, not only the constitution of the device is complicated but also the size of the device itself becomes large. Therefore, this development device is not preferable. Further, since it takes time for previously mixing, there is a fear that follow-up performance of toner concentration worsens (delay in time).